1. Field of the Invention
The present invention relates to a wheel unit.
2. Description of the Related Art
In a self-propelled electric appliance such as a cleaning robot, a wheel unit including a wheel and a motor that drives the wheel is mounted. For example, on the left and the right of an autonomous floor-cleaning robot 10 disclosed in Japanese Unexamined Patent Application Publication No. 2004-195215, main wheel subassemblies 42A and 42B are mounted. The main wheel subassembly of the related art includes wheels 42AW and 42BW attached to be rotatable and motors 42AM and 42BM which operate to drive the respective wheels (see, for example, paragraphs [0018] to [0021] and FIGS. 4 and 5 of Japanese Unexamined Patent Application Publication No. 2004-195215).
Hitherto, in this type of cleaning robot, a motor with a brush having large dimensions in an axial direction is used. When the motor and the wheel are arranged to be aligned in the axial direction, the dimensions of the wheel unit in the axial direction are increased. Therefore, in the related art, the motor is disposed on the outside of a ground surface of the wheel to reduce the dimensions of the wheel unit in the axial direction. Also in FIG. 4 of Japanese Unexamined Patent Application Publication No. 2004-195215, a state where the motors 42AM and 42BM are arranged on the outside of the ground surface of the wheel is illustrated.
However, when the motor is disposed on the outside of the ground surface of the wheel, the wheel unit is increased in size in a movement direction or a vertical direction. Therefore, the degree of freedom for a design of other parts of the cleaning robot is reduced. Therefore, there is a demand for a reduction in the dimensions of the wheel unit in the axial direction without an extension of the wheel unit in the movement direction or the vertical direction.
In contrast, in the wheel unit, a support structure for rotatably supporting a gear or the wheel is included. When the reduction in the size of the wheel unit is taken into consideration, there is a need to sufficiently ensure the durability of the support structure.